Multiple layer insulation for a cryogenic structure



P. JONES Aug. 20, 1968 MULTIPLE LAYER INSULATION FOR A CRYOGENICSTRUCTURE Filed OCt. 23, 1964 2 Sheets-Sheet 1 INVENTOR.

PE re-e J'o/vas P. JONES Aug. 20, 1968 MULTIPLE LAYER INSULATION FOR ACRYOGENIC STRUCTURE 2 Sheets-Sheet 2 Filed Oct. 23, 1964 INVENTOR.

P5 7222 J'o/vss BY I I United States Patent 3,397,720 MULTIPLE LAYERINSULATION FOR A CRYOGENIC STRUCTURE Peter Jones, Los Angeles, Calif.,assignor, by mesne assignments to Hitco, Gardena, Califl, a corporationof California Filed Oct. 23, 1964, Ser. No. 405,929 7 Claims. (Cl.138149) ABSTRACT OF THE DISCLOSURE A thermal insulation of alternatingplain reflective plastic sheets and dimpled plastic sheets, the dimplesbeing spaced apart along two directions substantially at right angles toeach other. Support means at each end of an insulation pack are providedto prevent contact of the insulation with inner or outer walls of aninsulated container.

This invention relates to a multiple layer insulation for a cryogenicpipe line, and particularly to the means to effectively preventexcessive heat transfer from the external atmosphere or room temperatureto the cryogenic material which is flowing within a spaced inner pipe orconduit. The cryogenic material referred to in this application may beliquid hydrogen, nitrogen, oxygen, or the like, all of which have a verylow temperature while in a liquid state.

My invention provides an effective means of insulating an inner conduitcarrying cryogenic material from an outer pipe or jacket whichsurround-s the conduit to prevent heat from being transferred from theoutside, or the atmosphere, to the cryogenic material whereby thatmaterial may be caused to vaporize. This means includes alternate layersof flat sunfaced reflective sheets, such as polyester film, separated bycorrugated or dimpled sheets of the same reflective polyester film.

Another object of my invention is to provide a novel insulation means ofthe character stated, whereby a plurality of superposed sheets aresupported at their ends by pads formed of glass fibers or otherinsulating material.

Another object of my invention is to provide an effective means to keepthe flat reflector sheets separated, so that the reflector layers do nottransmit heat by means of direct contact with each other.

Still another object of my invention is to provide a novel insulationmeans which is relatively inexpensive, and which requires a minimum oflabor to install. Furthermore, my insulation means provides sufiicientstrength and excellent resistance to external dynamic effects anddamaging vibrations. The entire assembly of the reflector sheets istotally separated from contact with either cold or warm surfaces. Thisis accomplished by the end supports which are formed of strong materialof low heat conductivity.

Other objects, advantages and features of invention may appear :from theaccompanying drawings, the subjoined detailed description and theappended claims.

In the drawing:

FIGURE 1 is a perspective view of one pair of superposed insulationsheets.

FIGURE 2 is a fragmentary view of an insulated pipe line embodying myinvention and with parts broken away to show interior construction.

FIGURE 3 is a transverse sectional view taken on line 3-3 of FIGURE 2.

FIGURE 4 is a fragmentary sectional view taken on line 4-4 of FIGURE 3.

FIGURE 5 is a fragmentary longitudinal sectional view taken on line 55of FIGURE 3.

FIGURE 6 is an enlarged transverse sectional View of the insulationwithin the area indicated by 6 in FIG- URE 5.

FIGURE 7 is a fragmentary vertical sectional view of a modified form ofinsulation sheet support.

Referring more particularly to the. drawing, the numeral 1 indicates aninner conduit which will be termed the cryogenic conduit. This conduitcarries the cryogenic material, such as liquid hydrogen, nitrogen,oxygen, or the like. An outer jacket 2 is spaced from the conduit 1 andis concentric with that conduit. The conduit 1 and the jacket 2 are bothmetallic pipes and of suflicient strength and thickness to carry theparticular load which is required. An annular space 3 is thus formedbetween the conduit 1 and the jacket 2 and this space is normallyevacuated to assist in the heat insulation of the inner conduit 1.Evacuation of the space 3 occurs after the insulation units (to besubsequently described) are in place and after all, or a substantialpart, of the entire conduit has been layed.

At intervals throughout the length of the conduit 1, I providesupporting annular rings 4, which are preferably formed of glass fibersor other similar somewhat porous material, but which has sufficientcompressive strength to support the conduit 1 'within the pipe or jacket2. The ring 4 is sufficiently porous so that air can readily passthrough it when the space 3 is being evacuated. A sleeve 5 is concentricwith the ring 4 and is positioned on the outside of the ring, extendingbetween the outer surface of the ring and the inner surface of thejacket 2. This sleeve 5 is also formed of glass fibers or other suitableporous material which has sufficient compressive strength. The sleeve 5and the ring 4 are slightly spaced at their adjacent faces by a spacerring 6. The spacer 6 is shorter than the ring 4 and sleeve 5 to provideannular grooves to receive the ends of annular insulation packs 7. Theinsulation packs 7 extend longitudinally between adjacent supportingrings 4, as shown, and these insulation packs are assembled in thefollowing manner: A flat faced polyester sheet 8 termed Mylar is coatedby a reflecting material such as silver. The flat sheets 8 are separatedby corrugated or dimpled sheets 9, which sheets are also formed of apolyester coated material termed Mylar. The corrugated or dimpled sheets9 have a permanent corrugation or dimple formed therein, and since thepolyester sheet is so formed that the corrugation or dimpling of thesheet will not flatten or diminish, due to normal weight, vibration, orthe like. The corrugated or dimpled separations, while contactingadjacent flat insulator sheet 8, will still not cause a heat flow ortransfer through the insulating pack, due to the fact that the points ofcontact are small and, furthermore, the corrugated or dimpled sheets arealso reflective structures, thus materially reducing the heat flow dueto contact. The dimples of the separating sheet 9 are spaced along twodirections which are disposed substantially at right angles to eachother. A characteristic of the polyester sheet termed Mylar is such thatno drying or baking cycle is required to dry moisture out of theinsulation. The composition of the polyester film precludes theabsorption of moisture or the entraprnent of gases. Also the dimpling orcorrugation of the polyester sheets 9 provides convenient escape routesor passages for atmospheric air which might be trapped between the flatsheets 8 and the dimpled sheets 9 during the vacuum pump down. Thesequalities of the polyester sheets and their construction as describedmaterially simplifies the maintenance of the required vacuum within thepipe line, and also materially simplifies this pump operation.

In FIGURE 7 I have illustrated a modified form of end support for theinsulating bundles of polyester sheets, consisting of an outer annularsupporting ring 10 which is formed with an inner annular groove 11. Apair of inner annular sleeves 12-13 are spaced longitudinally of theconduit 1 to provide an annular space 14. The ends of the adjacentinsulation packs 7 extend into the space between the rings 10 and thespaced sleeves 1213 as shown. To hold these packs 7 in position,particularly as to their adjacent abutting ends, I provide a shortlength of insulation 14 which fits in the groove 11. The insulation 14-is constructed in the same manner as the insulation pack 7 previouslydescribed. A second insulation pack 15 is positioned within the space14, and this insulation pack is also similar in construction to theinsulation pack 7 previously described. In this manner I provideadditional depth of insulation between the inner conduit 1 and the outerpipe or jacket 2. In this construction also there is a continuous packof insulation running longitudinally of the conduit and extendingthroughout the entire length of that conduit.

My method of suspending a dimpled polyester (Mylar) cryogenic insulationin pipe lines or in Dewars results in a stress-free system with a safetyfactor based on weight of the insulation of more than ten to one. Theinsulation qualities of metallized polyester sheets (Mylar) would neverdeteriorate in use, due to temperature, cycling or any other conditionsto be found in cryogenic applications. This means that a dimpled sheetof Mylar, as disclosed in this application, will be maintenance free forthe life of the equipment. There are also material advantages due to asavings in the cooled down process, due to a reduced mass in myinsulation.

In my method and structure as disclosed, no Mylar layers will toucheither a cold or warm surface of the evacuated space, thereby permittingonly a small temperature difference across the insulation packs 7 or thelayers thereof. This means according to the Stefan- Boltzmann law thatthe undesirable heat leak is brought to a minimum and is under acontrolled design environment.

tMy improved multiple layer insulation is applicable to cryogenicinstallations other than a pipe line, for example, this construction canbe used on cryogenic Dewar vessels, spaced chambers, as might beemployed in outer space, as 'well as vessels, containers, and the like,which either contain or house a cryogenic material, or with which toexclude an outer low temperature from the space within the vessel. Myinsulation construction can be employed in any vessel or pipe line withvacuum jacketin g.

Having described my invention, I claim:

1. A multiple layer insulation in combination with a cryogenic pipe linecomprising,

an inner pipe conveying a cryogenic material,

an outer jacket surrounding the inner pipe and radially spacedtherefrom,

an insulation pack in said space comprising superimposed sheets ofreflective plastic material formed as cylinders surrounding the innerpipe,

said insulation pack comprising alternate plain surfaced sheets ofreflective plastic material separated by a dimpled sheet of reflectiveplastic material which dimples make small points of contact with a 4said plain surfaced sheets and wherein said dimples are spaced apartalong two directions disposed substantially at right angles to eachother,

and annular insulative and porous supporting rings surrounding the innerpipe and longitudinally spaced thereon,

said annular supporting ring having means thereon to receive one end ofan insulation pack to support said insulation pack in spaced relation toboth said inner pipe and said outer jacket.

2. A multiple layer insulation in combination with a cryogenic pipe linecomprising,

an inner pipe conveying a cryogenic material,

an outer jacket surrounding the inner pipe and radially spacedtherefrom,

an insulation pack in said space comprising superimposed sheets ofreflective plastic material formed as cylinders surrounding the innerpipe,

said insulation pack comprising alternate plain surfaced sheets ofreflective plastic material separated by a dimpled sheet of reflectiveplastic material which dimples make small points of contact with saidplain surfaced sheets and wherein said dimples are spaced apart alongtwo directions disposed substantially at right angles to each other,

and annular insulative and porous supporting rings surrounding the innerpipe and longitudinally spaced thereon,

said annular supporting ring having means thereon to receive one end ofan insulation pack to support said insulation pack in spaced relation toboth said inner pipe and said outer jacket,

said means comprising an annular groove in the end of the supportingring into which the end of the insulation pack fits.

3. An assembly comprising:

(a) a container having spaced inner and outer walls;

and

(b) thermal insulation packs extending between said walls and beingspaced therefrom;

(c) each of said packs including opposed and spaced essentially planar,radiation-reflecting sheets; and (d) a separator sheet intermediate eachpair of said reflecting sheets,

(c) said separator sheet being formed to provide dimples facing eachpair of said reflecting sheets which dimples make small points ofcontact with said reflecting sheets,

(f) said dimples being spaced apart along two directions of saidseparator sheet disposed substantially at right angles to each other;and

(g) thermal insulative support means interfitting edge portions of saidpacks for holding said packs in spaced relation to said walls.

4. The assembly defined in claim 3 in which said support means comprisesporous material, the space between said walls being at a pressuresubstantially below atmospheric pressure.

5. The assembly defined in claim 3 in which each of said sheets consistsof plastic film having a radiationreflecting metallic coating on theouter film surfaces.

6. A thermal insulation packing comprising:

(a) opposed and spaced essentially planar, radiationreflecting sheets;and

(b) a separator sheet disposed intermediate each pair of said reflectingsheets,

(c) said separator sheet being formed to provide dimplies facing eachpair of said reflecting sheets which dimples make small points ofcontact with said reflecting sheets, and said dimples being spaced apartalong two directions of said separator sheet disposed substantially atright angles to each other, and

(d) porous, thermal insulative support means interlitting edge portionsof: the packing for holding the packing between and in spaced relationto inner and outer walls of a container.

7. The packing defined in claim 6 in which each of said sheets consistsof plastic film with a metallic, radiation-reflecting coating on theouter surfaces of said film.

References Cited UNITED STATES PATENTS 683,514 10/1901 Stephens 138-4481,987,798 1/1935 Ruppricht 161137 X 2,179,057 11/1-939 Schuetz 138148 X10 LAVERNE D. GEIGER, Primary Examiner.

C. L. HOUCK, Assistant Examiner.

